There exists a need for dispensing in precisely metered amounts various types of high viscosity or gel-like medicinal and dental compositions, such as Pilocarpine which is an anti-glaucoma agent normally dispensed in doses as small as 10 to 15 .mu.l.
One type of dispenser capable of dispensing the aforesaid compositions comprises an elongate hollow body from which the composition can be metered through a closable discharge opening by longitudinally advancing within the body a piston attached to a threaded spindle. The spindle engages a nut mounted on a rear end of the body. A flange provided on the nut has indicia cooperating with an orientation wing mounted to rotate the spindle. The amount of composition to be dispensed is controlled by the user who rotates the wing into registration with one of the indicia displayed on the flange.
As the amount of dispensed composition is controlled by user sight alignment between the orientation wing and indicia, the metering accuracy is dependent on how exact the wing is set to the respective indicia. Accurate metering thus requires careful handling of the device. There is also a chance of the spindle being screwed out of the hollow body due to careless handling, inadvertent actuation or shock, resulting in an amount of composition corresponding to only an incomplete revolution being dispensed during subsequent rotation of the spindle.
Another problem associated with the foregoing device is that one hand is required to rotate the spindle while the other hand holds the body to dispense the composition. Two handed operation can be cumbersome and particularly difficult for arthritic persons.
To accurately dispense a desired amount of high viscosity composition, U.S. Pat. No. 4,189,065 to Herold discloses a dispensing device wherein a hollow cylindrical body containing composition is formed with a stationary detent engageable with a longitudinal groove provided on a threaded spindle to precisely control the degree of angular rotation of the spindle when rotating a knob mounted thereon to dispense the composition. While this type of device provides greater metering accuracy than the aforementioned dispenser, two handed operation is still required to discharge composition, one hand grasping the body while the other hand rotates the knob. Also, since the detent is a resilient member, it is possible for the groove to overtravel slightly past the detent during rotation of the spindle, due to the resiliency of the latter, causing an excessive amount of compositions to be discharged from the dispenser.
It is accordingly an object of the present invention to provide an improved metering dispenser for high viscosity compositions which allows precise metering utilizing simple means.
A further object of the invention is to provide a device achieving exact metering by utilizing a mechanism capable of single-handed operation.
It is another object to provide a device for dispensing high viscosity compositions which precisely controls metering by automatically stopping advancement of a plunger means after a precise amount of composition has been dispensed.
Still a further object is to provide a metering dispenser which is easy to manufacture and safe to handle.